U.S. Pat. Nos. 4,588,229 and 4,726,624 to Jay (as well as other Jay patents), describe and claim seat cushions for wheelchairs which comprise a combination of a fluid-filled, segmented pad juxtaposed over a relatively rigid, shaped supporting base or tray. The aforesaid Jay patents teach the manufacture of the tray from polyurethane foam, which may be formed in a process which provides a self-skinned polyurethane film on the surface of the foam. The wheelchair seat cushions described in the Jay patents have been commercialized using integral skin polyurethane foam trays, and these seat cushions have proved to be an enormous commercial success. However, integral skin polyurethane foam trays are relatively heavy and consequently these prior art seat cushions are also relatively heavy. Furthermore, most molded integral skin polyurethane foams contain an open-celled structure underneath the skin which is prone to moisture or urine absorption if the skin is damaged or cut. Tray modifications are common to accommodate specialized user needs, such as cutouts for the wheelchair seat rails to lower the cushion in the chair, or trimming the edges of the tray to narrow the cushion to fit a particular wheelchair. Non-integral-skin urethane foam may be used but a sealant must be painted over the surface to prevent moisture or urine absorption and the same modification problems exist.
The cushions of the present invention are significantly lighter than the prior art cushions based on polyurethane foam trays. For example, a standard sized seat cushion base, made in accordance with the present invention weighs less than 50% of the weight of the same size seat cushion base made from the prior art polyurethane foam. Because these trays are designed to be used as components of wheelchair cushions and wheelchairs are usually propelled by the wheelchair users, any reduction in weight is a great advantage. Many wheelchair users have impaired function of their upper extremities, thus making for difficulties in grabbing, handling, or otherwise lifting heavy objects. The wheelchair cushion is usually transferred from one seating surface to another by the user and, therefore, must be light weight.